(a) Field of the Invention
The present invention relates to a preparation method of an acryl-based impact-reinforcement, and more particularly, to a preparation method of an acryl-based impact-reinforcement, in which latex having large particles and latex having small particles are blended together to enable the enhancement of an impact-resistance of a polyvinylchloride (PVC) resin.
(b) Description of the Related Art
An impact-reinforcement is used for enhancing the impact-resistance of the polyvinyl chloride resins, and the different types of impact-reinforcement include a methyl methacrylate-butadiene-styrene-based (MBS) resin, a chlorinated polyethylene-based (CPE) resin, and an acryl-based resin. Among these resins, the acryl-based resin is widely used for products exposed to the sun, since it has a high weather-resistance. For example, PVC window sash needs both high impact-resistance and weather-resistance, and impact reinforcement which is prepared by grafting a rubbery elastomer core comprising alkyl acrylate polymer with a glassy methacryl-based polymer shell that is highly compatible to the PVC resin showed both necessary properties.
The manner in which the core is bonded with the shell chemically is a critical factor in realizing beneficial properties of acryl-based impact reinforcements with the core-shell structure. In addition, the degree of cross-linking of dispersed rubber particles in matrix, the content of rubber particles, the size of rubber particles, and the swelling index of rubber particles to solvent are critical factors that affect the impact resistance of acryl-based impact reinforcements.
In order to enhance the impact resistance of polyvinyl chloride resin, an acryl-based impact reinforcement has been prepared by emulsion polymerization which includes both core and shell polymerization.
In the core polymerization, alkyl acrylate monomers having one double bond and low glass transition temperature are polymerized, and the alkyl acrylate polymer gives an acryl-based impact reinforcement with both weather-resistance due to the absence double bond after polymerization and impact-resistance due to the low glass transition temperature. Cross-linking agents give impact resistance to the impact reinforcement due to the formation of the rubber structure on the impact reinforcement. The cross-linking agent also provides a latex stability during the polymerization reaction, and it enables the core to maintain a spherical form during the processing steps.
The shell polymerization is generally performed by graft-polymerizing alkyl methacrylate monomer, which is highly compatible with polyvinyl chloride resin, on the core. To increase a dispersibility of the impact-reinforcement, the shell may contain small amount of an acrylonitrile monomer.
Two preparation methods of the acryl-based impact reinforcement, which is prepared by emulsion polymerization, are disclosed. U.S. Pat. No. 5,612,413 discloses a method, in which the impact reinforcement is prepared by multi-step-emulsion polymerization that includes polymerization of a seed having small particles, polymerization of monomers in two or four steps to grow the seed, and polymerization of monomers used for a shell therein in order to form a core-shell structure wherein the core is enclosed within the shell. European Patent No. 0,522,605A discloses a method, in which an impact reinforcement is prepared by a micro-agglomeration method comprising polymerizing a latex having a core-shell structure with a particle size of 100 nm or less, agglomerating the particles to prepare a latex with a desired particle size, and forming a capsulated shell on the agglomerated particles.
However, there is a need to develop an impact reinforcement which have an enhanced impact resistance to be used in place of the impact reinforcement prepared by the conventional method.